Method for preparing dual colloid compositions
Disclosed is a method for preparing dual colloid catalyst compositions which are suitable for use in such processes as ammonia synthesis, carbon monoxide hydrogenation, hydrogenation and denitrogenation. The method comprises forming a gel, or suspension, by admixing: (i) one or more transition metal cyano-containing anionic-complex solutions wherein at least one solution contains a reducible transition metal, and wherein one or more of these solutions optionally contains a nonreducible metal, with (ii) one or more solutions containing polyovalent metal cations. The resulting gel, or suspension is heated at a temperature of about 90.degree. C. to about 150.degree. C. for an effective amount of time to allow hydrolysis and polymerization to occur. The resulting solid is then separated and dried.
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The present invention relates to a method for preparing dual colloid catalyst compositions which are suitable for use in such processes as ammonia synthesis, carbon monoxide hydrogenation, hydrogenation and denitrogenation. The method comprises forming a gel, or suspension, by admixing: (i) one or more transition metal cyano-containing anionic-complex solutions wherein at least one solution contains a reducible transition metal, and wherein one or more of these solutions optionally contains a nonreducible metal, with (ii) one or more solutions containing polyvalent metal cations. The resulting gel, or suspension is heated at a temperature of about 90.degree. C. to about 150.degree. C. for an effective amount of time to allow hydrolysis and polymerization to occur. The resulting solid is then separated and dried.
BACKGROUND OF THE INVENTIONBecause of their almost incalculable value to industrial chemical processes, many catalysts and catalytic processes have been developed over the years. Catalysts, such as heterogeneous catalysts, can generally be classified as either supported metal catalysts or massive metal catalysts, also sometimes referred to as bulk metal catalysts.
Supported metal catalysts are usually comprised of relatively small metal crystallites on relatively large support particles. The support particles may also act as a promoter for the active ingredients of the catalyst. Because of metal crystallites are small compared to the support particles, the effective metal surface area per unit volume of catalyst is relatively small, thus limiting the activity of the catalyst.
In contrast, massive metal catalysts, such as the well known magnetite or spinel-based ammonia synthesis catalysts, or Raney metal type catalysts, generally contain metal domains having dimensions which are usually far greater than any promoter phase particles which may be present. The effective metal surface area per unit volume of such catalysts is also relatively small, thus limiting the potential activity of the catalyst. To maximize the effective catalytically active surface area per unit volume, it would be desirable to produce a catalyst having a median metal crystallite, or domain, size of about 25 .ANG. to about 500 .ANG. in diameter. The desired crystallite size, of course, depends on the intended application. For example, crystallite sizes in the range of 25 .ANG. to 250 .ANG. are desired for catalyzing reactions involving relatively small substrate molecules, while larger crystallites, in the range of 250 .ANG. to 500 .ANG., are desired for catalyzing reactions involving large substrate molecules. Effective metal surface area per unit volume of catalyst as used herein means metal area accessible to reactants. Because of the demanding nature of certain catalytic reactions (e.g. ammonia synthesis) the surface area of very small metal crystallites may be either ineffective or non-selective.
Although it may be possible to conventionally produce supported metal catalysts containing metal crystallites having a median diameter within the 25 .ANG. to 500 .ANG. range, it can only be done in combination with relatively large support particles or a relatively large pore support, far in excess of the metal crystallite diameter. Consequently, the effective metal surface area suffers and a catalyst is produced having less activity then it would otherwise have if the size of the support particles were comparable to the size of the metal crystallites.
Consequently, there is a need in the art for the development of catalysts characterized as being balanced with respect to metal surface area and metal crystallite size. That is, catalysts having improved activity owing to their tendency to maximize the effective surface area per unit volume of catalyst.
SUMMARY OF THE INVENTIONIn accordance with the present invention, there is provided a method for preparing catalyst precursor compositions, which method comprises:
(a) forming a gel or suspension by admixing (i) one or more transition metal cyano-containing anionic-complex solutions wherein at least one solution contains one or more reducible transition metals selected from Groups IB, IIB, VIB, VIIB, and VIII of the Periodic Table of the Elements, wherein the cations accompanying the anionic complexes may be one or more alkali metal ions, with (ii) one or more solutions containing metal cations wherein at least one of the metals is a nonreducible metal selected from the group consisting of Cr, Al, Th, U, the lanthanides, and elements of Group IIA of the Periodic Table of the Elements;
(b) heating the resulting gel, or suspension, at a temperature of about 90.degree. C. to about 150.degree. C. for an effective amount of time to allow hydrolysis and polymerization to occur;
(c) separating and drying the resulting solid precursor.
DETAILED DESCRIPTION OF THE INVENTIONThe catalyst compositions of the present invention are comprised of about 15 to about 85 wt.% of metal crystallites interspersed with about 15 to about 85 wt.% of promoter particles which compositions are sometimes referred to herein as dual colloid catalysts because the sizes of the metal crystallites and the promoter particles are both of colloid size and are within about an order of magnitude of each other. For example, the size of the metal crystallites are such that at least about 80% will have a diameter, d, between about 25 .ANG. and 500 .ANG. with the proviso that the crystallite size distribution of at least about 80% of these be expressed by the relationship 0.5<d<2D where D is the median of the diameters of this 80%.
The metal crystallites of the catalysts of the present invention may be comprised of one or more of the following: (a) a single transition metal, (b) two or more metals, including alloys, wherein at least about 50 wt.% of the metal content is one or more transition metals, and (c) one or more reducible transition metal carbides, nitrides, and oxides. The term, reducible, as used herein for the metal crystallites means converted to the metallic state by hydrogen at temperatures up to about 650.degree. C. and at hydrogen pressures up to about 300 atm. where the ratio of hydrogen partial pressure to the partial pressure of water, CH.sub.4, and NH.sub.3 is at least 1000:1. The transition metal may be selected from those reducible metals from Groups IB, IIB, VIB, VIIB, and VIII of the Periodic Table of the Elements, as illustrated on the inside cover of Handbook of Chemistry and Physics, 55th Edition, CRC Press 1974-1975. Preferred transition metals, especially for use in ammonia synthesis, include Mo, Re, W, Fe, Ru, Os, Co, Rh, and Ni. Of course, the choice of transition metals will depend on the reaction being catalyzed.
X-ray photoelectron spectroscopy of activated catalysts prepared from K.sub.4 Ru(CN).sub.6 such as materials analogous to those described in examples 5 and 6 hereof showed no evidence of the presence of metallic potassium in the promoter phase which is interspersed with the crystallites of the present invention. The promoter phase is comprised of about 15 to about 85 wt.% of a nonreducible promoter phase interspersed with the metal crystallites and containing at least one element selected from the group consisting of Cr, Mn, Zn, Al, Si, Th, U, the lanthanides, and Groups IA, IIA, IIIB, IVB, and VB of the Periodic Table of the Elements, wherein the promoter phase is comprised of particles of which at least about 80% have a diameter between about 15 .ANG. and 1500 .ANG. wherein the median diameter (D) of the metal crystallites and the median diameter of the 80% of the promoter particles do not differ by more than a factor of about 20.
The nonreducible materials impart improved activity, selectivity, and/or stability to the catalyst. The term, nonreducible material, as used herein for the promoter phase, means a material which is not reduced to the metallic state when subjected to the atmosphere and process conditions under which it will be employed. That is, the particles of the promoter phase are not catalytically active in the sense that the metal crystallites are, although they may perform a different catalytic function than the metal crystallites for any particular reaction. Non-limiting examples of material which may comprise the promoter phase herein include the structural promoters such as the refractory metal oxides, Al.sub.2 O.sub.3, MgO and CaO, metal nitrides, and metal carbides. Also included are electronic promoters such as the oxides, nitrides, amides and hydroxides of metals having a Pauling electronegativity of 1.3 or less. The promoter phase of the precursor may also contain compounds of the promoter elements, such as halides, carbonates, nitrates, nitrites, phosphates, sulfates, etc. It is preferred that such promoter compounds be chosen such that their anions not give rise to materials which will poison the active catalyst. For example, a precursor containing sulfates would be undesirable for activation and use for ammonia synthesis. The particular material chosen for the promoter phase will primarily depend on the reaction in which it is used. For example, if the promoter is used for a catalyst for ammonia synthesis, it is preferred that the promoter phase be highly basic and include compounds of one or more metals selected from the group consisting of the alkali metals, the alkaline-earth metals, and lanthanum. Of course, the promoter phase of the catalysts of the present invention is not restricted to any particular type of promoter. They may, in fact, function as more than one type, for example, a promoter may serve as both a structural and an electronic promoter, such as MgO.
Individual promoter particles may become indistinguishable through the formation of a more or less continuous network of promoter since the promoter is often amorphous or not very crystalline. In this case the separation between adjacent metal crystallites caused by the promoter phase may vary from about 15 .ANG. to about four times the median diameter of the metal crystallites. The promoter phase may contain alkali, alkaline earth or lanthanide cyanide.
The term "promoter phase" as used herein includes particles of a single composition as well as particles of different compositions.
The metal crystallite phase of the catalyst of the present invention may be represented by A.sub.a B.sub.b C.sub.c D.sub.d E.sub.e F.sub.f G.sub.g, and the nonreducible promoter phase may be represented by H.sub.h I.sub.i J.sub.j K.sub.k L.sub.l Al.sub.m Si.sub.s, where:
A is one or more of Fe, Ru, Os and a is from 0 to 4;
B is one or more of Co, Rh, Ir and b is from 0 to 4;
C is one or more of Ni, Pd, Pt and c is from 0 to 4;
D is one or more of Re, Mo, W and d is from 0 to 2;
E is one or more of Mn, Cr and e is from 0 to 0.5;
F is one or more of Cu, Ag, Au and f is from 0 to 2;
G is one or more of Zn, Cd and g is from 0 to 1;
wherein the values of d, e, and g are such that the metals of D, E, and G will be reduced to the metallic or metal alloy state under reducing conditions when in combination with metals of A, B, C, and F in amounts of a, b, c, and f, and wherein the sum a+b+c+d+e+f+g is between 1 and 4, and
H is one or more of Be, Mg, Ca, Sr, Ba and h is from 0 to 4;
I is one or more of Li, Na, K, Rb, Cs, and i is from 0 to 4;
J is one or more of Sc, Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Th, U and j is from 0 to 4;
K is one or more of Ti, Zr, Hf, V, Nb, Ta, and k is from 0 to 4;
L is one or more of Cr, Mn, Zn and l is from 0 to 4, where the value of l is such that Cr, Mn, and Zn are not reduced to the metallic or metallic alloy state when in combination with metals of A, B and C in amounts a, b, c under reducing conditions, and m and s are each from 0 to 2, wherein the sum h+i+j+k+l+m+s is between 0.1 and 4.
A preferred class of catalyst compositions of the present invention may be represented by the formula:
Fe.sub.a Co.sub.b Ni.sub.c Ru.sub.d -H.sub.h I.sub.i J.sub.j K.sub.k L.sub.l Al.sub.m Si.sub.s
where
H is one or more of Mg, Ca, Sr, Ba and h is from 0 to 2;
I is one or more of Li, Na, K, Rb, Cs and i is from 0.1 to 4;
J is one or more of Y, La, Ce, Eu, Th, U, and the remaining lanthanides and j is from 0 to 3;
K is one or more of Ti, Zr, Hf, Nb, Ta and k is from 0 to 2;
L is Cr and l is from 0 to 2;
a is from 0 to 3, b is from 0 to 0.5, c is from 0 to 0.5, d is from 0 to 3, and m and s are each from 0 to 2.
Preferred species of this class include: (a) b, c, d, j and s each being equal to 0, a being from 1 to 3, i being from 0.1 to 3, m being from 1 to 2, and I being one or more of Na, K, Rb, and Cs; (aa) same as (a) above except h being equal to 0; (b) b, c, d, m and s each being equal to 0, a being from 0.1 to 3, i being from 0.1 to 3, and l being from 0.1 to 3; (bb) same as (b) above except h being equal to 0; (c) b, c, d, l, m and s each being equal to 0, a being about 1 to 3, i being from 0.1 to 3, j being from 0.1 to 3, and J being one or more of La and Ce; (cc) same as (c) above except h being equal to 0; (d) a, b, c, j and s each being equal to 0, d being from 1 to 3, i being from 0.1 to 3, m being from 1 to 2, and I being one or more of Na, K, Rb, and Cs; (dd) same as (d) above except h being equal to 0; (e) a, b, c, m and s each being equal to 0, d being from 1 to 3, and i being from 0.1 to 3; (ee) same as (e) above except h being equal to 0; (f) a, b, c, l, m and s each being equal to 0, d being from 1 to 3, j being from 1 to 3, and J being one or more of La and Ce; and (ff) same as (f) above except h being equal to 0.
Another preferred class of catalyst compositions of the present invention may be represented by the formulas:
A.sub.a B.sub.b C.sub.c D.sub.d E.sub.e -H.sub.h I.sub.i J.sub.j K.sub.k L.sub.l Al.sub.m N.sub.n
where:
A is one or more of Fe, Ru and a is from 0.01 to 2;
B is Co and b is from 0 to 0.4;
C is Ni and c is from 0 to 0.4;
D is one or more of Mo, W and d is from 0 to 2;
E is Mn and e is from 0 to 0.5;
H is one or more of Mg, Ca, Sr, Ba and h is from 0.2 to 3;
I is one or more of Li, Na, K, Rb, Cs and i is from 0.1 to 3;
J is one or more of La, Ce and j is from 0 to 2.0;
K is one or more of Ti, Zr, Hf, Nb, Ta and k is from 0 to 2;
L is Cr and l is from 0 to 2;
N is one or more of Si, Y and n is from 0.5 to 2.0; and
m is from 0.5 to 2.0.
In more preferred species of the above the metal crystallite phase is Fe, alone or in combination with one or more of Co, Ni, Mo, W, or Mn, preferred molybdenum and tungsten.
Another preferred class of catalyst compositions of the present invention may be represented by:
Fe.sub.a Co.sub.b Ni.sub.c Ru.sub.d -H.sub.h I.sub.i J.sub.j K.sub.k L.sub.l Al.sub.m N.sub.n
where;
H is one or more of Mg, Ca, Sr, Ba and h is from 0 to 3;
I is one or more of Li, Na, K, Rb, Cs and i is from 0 to 1.0,
J is one or more of La, Ce and j is from 0 to 2.0;
K is one or more of Ti, Nb, Ta, Zr and k is from 0 to 3;
L is one or more of Cr, Mn Zn and l is from 0 to 3;
N is one or more of Si, Y and n is from 0 to 3;
a, b, c, d and m are from 0 to 3, wherein the sum a+b+c+d=0.5 to 4, and the sum k+l+m+n=0.1 to 4.
The dual colloid catalyst compositions of the present invention are prepared by mixing under sufficient agitation of: (i) one or more transition metal cyano-containing anionic-complex solutions wherein at least one solution contains a reducible transition metal selected from the group consisting of Groups IB, IIB, VIB, VIIB, and VIII of the Periodic Table of the Elements and wherein one or more of these solutions optionally contains a nonreducible promoter phase metal, with (ii) one or more solutions containing polyvalent metal cations wherein at least one of the metals is a non-reducible promoter phase metal and wherein one or more of these solutions optionally contains a cationic form of a reducible metal as referred to above. The solutions of (i) and (ii) above must be sufficiently concentrated so as to form a gel or a colloidal suspension, but not too concentrated than an intractable solid will form. It is preferred that the number of ion equivalents of (i) and (ii) be substantially the same. Preferably, the pH of each solution is such that the admixture of the two solutions has a pH of about 3.5 to about 7, more preferably between about 4 to about 7. A preferred way of providing the pH is by adjusting the pH of the second solution (ii) relative to the pH of the first solution (i) to give the desired pH of the admixture. Of course, the final solution may also be adjusted with the appropriate amount of acid or base to the desired pH.
The temperature at which the solutions are mixed is an effective temperature. That is, a temperature not too high that it will adversely affect the morphology of the resulting catalyst precursor and not too low that the solution freezes. Preferably, the solutions are mixed at about room temperature, approximately 20.degree. C. It is to be understood that the term "mixing" may be interchangeable with the term "reacting" because the solutions react with each other immediately when mixed. Consequently, mixing is performed for an effective amount of time, generally no more than a few minutes at about room temperature.
After mixing is completed, the admixture is heated either at atmospheric pressure or in an autoclave at a temperature from about 90.degree. C. to about 150.degree. C. It is convenient to conduct the heating under reflux conditions and it is preferred that the heating be done under an inert atmosphere to prevent excessive contamination of the reacting mixture and to prevent excessive oxidation. Heating is conducted for an effective amount of time to allow hydrolysis and polymerization to occur. By effective amount of time we mean that amount of time required to convert the insoluble, or sparingly, salts of the transition metal cyano-containing anionic-complex to the catalyst precursor. This precursor is comprised of one or more polymeric cyano complexes which on activation give rise to the active phase, and one or more hydrous oxide or polymeric hydroxide phases which on activation give rise to the promoter phase. Generally, the amount of time will be from about 10 to about 100 hours, preferably from about 15 to about 50 hours.
During heating, as the reaction proceeds, the pH of the mixture may change, usually becoming more basic. The pH may be adjusted; (a) by the addition of acid or (b) by the addition of acidic components such as metal salt solutions. During precursor formation and when an acidic pH is no longer needed, basic components such as Si or Nb, in the form of soluble silicates, niobates etc., may be added. The precursor formation reaction sequence can be followed by obtaining infrared spectra or X-ray powder diffraction patterns of the solid material.
After heating is completed, the suspension may be optionally mixed with another colloidal suspension containing one or more of the following non-limiting materials: SiO.sub.2, Y.sub.2 O.sub.3, Al.sub.2 O.sub.3 or with a slurry of a more traditional support such as gamma Al.sub.2 O.sub.3 etc. If a slurry of conventional support is used the resulting catalyst is a supported dual colloid catalyst and the dimensions set forth herein to describe the promoter phase of the catalyst compositions hereof do not apply to the added traditional support material.
Furthermore, the solids are recovered from the suspension by filtration or centrifugation/decantation. The resulting solid material may be washed by resuspension to remove soluble salts formed during the precursor reaction sequence.
The resulting moist solid is formed, such as by extrusion before drying or dried and formed by pelletizing. It is prefrred to dry the material at a temperture from about 50.degree. C. to 150.degree. C. in the absence of air.
It is within the scope of this invention that additional metal and promoter species be introduced onto the precursor methods such as by impregnation. Non-limiting examples of such species include: ReO.sub.4.sup.-, MoO.sub.4.sup.-2 and WO.sub.4.sup.-2.
The composition of the moist or dried solid material may be modified by ion-exchange. Both alkali and alkaline-earth metal ions present in the solid may be exchanged to some extent by any suitable ions depending on the intended use of the resulting catalyst. Non-limiting examples of such ions include: Li.sup.+, Na.sup.+, K.sup.+, Rb.sup.+, Cs.sup.+, NH.sub.4.sup.+, Ag.sup.+, Mg.sup.+2, Ca.sup.+2, Sr.sup.+2, Ba.sup.+2, La.sup.+3, Ce.sup.+3, Eu.sup.+3, and ZrO.sup.+2. These ions are contained in solutions having a preferred molarity of about 0.1 to 2.0 except where solubility limitations create an exception. The temperature of exchange can be from 0.degree. C. to the boiling point of the solution with 20.degree. to 60.degree. C. preferred.
This ion-exchange procedure is conducted for the purpose of preparing improved catalysts for certain processes. For example, an ammonia synthesis catalyst comprised of FeCo-KAlMg was improved by partially ion exchanging NH.sub.4.sup.+ for K+ and Ca.sup.+2 for Mg.sup.+2. This resulted in improved stability and greater volumetric activity.
When the catalyst composition is to be used in such processes as ammonia synthesis or hydrogenation it must be activated by reduction. This is preferably done by maintaining it at a temperature of about 150.degree. C. at a space velocity of greater than 5000 v/v/hr for a few minutes to several hours. The pressure is then increased preferably to about 1 mPa to 10 mPa, if it is not already at such a pressure, and the temperature is increased (at a rate of about 1.degree. to 30.degree. C. per hour) to about 315.degree. C. to about 360.degree. C., and holding it at that temperature until activation is complete. This can take from several hours to several days. In some cases additional slow heating to about 500.degree. C. may be required, for example, when more difficult to reduce metals are present or where reduction of metal oxides is involved. The temperature, pressure, and gas hourly space velocity may then be adjusted to the desired operating conditions for the catalytic reaction. Further heating to operating conditions should be in a moderately (<1.degree. C./min.) controlled manner. Heating the material too rapidly to a high temperature of, e.g., 400.degree. C. or more, without a sufficient exposure to moderate temperatures of, e.g., 150.degree. C. to 360.degree. C., will result in a material having poor catalytic activity for ammonia synthesis. The optimum reduction conditions, i.e., temperature, pressure, space velocity and heating rate, will depend on the catalyst composition and its intended use. The best temperature program for a given dual colloid catalyst of the present invention can often be determined by thermogravimetric analysis and high pressure thermogravimetric analysis tests. Such tests are well known to those skilled in the art and will not be discussed in detail herein.
The active catalyst may be used in the ammonia synthesis reaction directly without removal from the activation reactor. Alternatively, the activated and stabilized catalyst may be removed from the activation reactor and charged, or pelletized and charged, into a different reactor for use. This may be advantageous because activation of the composition generally results in approximately a 10 to 50% decrease in volume. Non-limiting examples of types of ammonia synthesis reactors which may be employed herein include vertical, horizontal, or radial-flow types which utilize the catalyst as a fixed bed, fluid bed, or the like.
The ammonia synthesis reaction herein is conducted according to procedures well known to those skilled in the art. Thus, nitrogen and hydrogen are passed over the catalyst at elevated temperatures and pressures sufficient to convert at least a portion of the nitrogen and hydrogen to ammonia.
The gaseous mixture of hydrogen and nitrogen which is introduced into the reactor preferably contains hydrogen and nitrogen in a volume ratio of 1:3 to 10:1, respectively, more preferably 1:1 to 4:1. Most preferred, however, is about a stoichiometric volume ratio of 3:1, except in the case of certain ruthenium-containing catalysts for which a nitrogen-rich feed gas is preferred.
The space velocity of the gaseous mixture of nitrogen and hydrogen expressed as volumes of gas at standard conditions per unit volume of catalyst per hour (GHSV), may range from about 1000 to 100,000 v/v/hr or more, depending on the reactor design. Preferred is about 5000 to about 60,000 v/v/hr.
The pressure of the gaseous feedstream for ammonia synthesis will generally be in the range of 0.1 to 30 MPa, preferably, from about 4 to 20 MPa.
For ammonia synthesis at high temperatures (>350.degree. C.) catalysts containing less than 7 wt.% potassium are preferred.
Highly active dual colloid catalysts usually require that the gas used in ammonia synthesis contain less than 5 ppm, preferably less than 1 ppm, H.sub.2 O, CO, CO.sub.2, or O.sub.2 and be esssentially free of sulfur containing compounds. High levels of impurity cause decreased catalyst life.
The ammonia in the product stream may be collected, separated, and purified by any methods known in the art for ammonia recovery.
The compositions herein, both precursor and activated catalyst, may also be used in CO hydrogenation wherein carbon monoxide and hydrogen are contacted with the compositions at elevated temperatures and under conditions sufficient to convert at least a portion of the carbon monoxide and hydrogen to hydrocarbons such as methane, ethane, propane, propylene, and the like, as well as oxygenates such as methanol, ethanol, propanol and the like. When the compositions are used for CO hydrogenation the transition metals of the compositions need not be in the metallic state. The practitioner skilled in the art of CO hydrogenation will know the conventional conditions under which such reactions may be catalyzed, and all such conditions are applicable herein. One patent describing a technique which may be used for this purpose is U.S. Pat. No. 2,735,362 which is incorporated herein by reference.
The following examples serve to more fully describe the manner of making and using the abovedescribed invention, as well as to set forth the best modes contemplated for carrying out various aspects of the invention. It is understood that these examples in no way serve to limit the true scope of this invention, but rather, are presented for illustrative purposes.
EXAMPLE 1 (COMPARATIVE)Catalyst A was prepared in accordance with the teachings of U.K. Pat. Nos. 253,122 and 273,735 to Uhde. Specifically, the composition was prepared as follows: A solution containing 66.7 g AlCl.sub.3 dissolved in 500 ml H.sub.2 O was rapidly mixed with a solution containing 211.8 g K.sub.4 Fe(CN).sub.6.3H.sub.2 O dissolved in 1000 ml H.sub.2 O. The resulting suspension had a pH of about 5.0 to 5.5 and began to gel almost immediately. It was transferred to a 2 liter flask and heated in an oil bath, to a temperature of about 80.degree. C. Under the application of a slight vacuum, water removal began. The vacuum was gradually increased to about 10.sup.-3 torr as the viscous gel dried. This procedure took about six hours. The resulting pale greenish yellow solid catalyst precursor was cooled under vacuum. It turned blue upon exposure to air. A sample of this precursor was activated under 75% H.sub.2 /25% N.sub.2 at a gas hourly space velocity of 5000. The reactor temperature was increased from room temperature (25.degree. C.) to 70.degree. C., and then at to 150.degree. C. at 99.degree. C./hr. After about 15 minutes at this temperature, the pressure was increased to 4.2 MPa and a 12.degree. C./hr upramp to 390.degree. C. was started.
After several hours at about 390.degree. C., a representative sample of the activated catalyst was examined by high resolution electron microscopy (HREM). Large rod-like structures, some 1600 .ANG. wide by 5000 to 10,000 .ANG. long, with possibly a laminar structure, were observed. Mixed with these rod-like structures were irregular regions, about 800 .ANG. to 3000 .ANG. across when seen at 125,000 magnification. At 700,000 magnification some of these were seen to be porous with about 100 .ANG. to 400 .ANG. pores. These appeared to be free of metallic particles. Other irregular regions contained numerous, relatively large Fe particles ranging in size from about 300 .ANG. to 900 .ANG. with most being between about 400 .ANG. and 600 .ANG.. Only about 10 to 20% of the large irregular regions were made up to about 120 .ANG. to 400 .ANG. metal crystallites interdispersed with similar sized non-metallic particles. Thus, most of the metal appeared to be in particles greater than 300 .ANG. in size. Elemental analysis of the activated catalyst revealed that it had the following composition (wt.%): Fe 13.84, Co 0.073, K 26.49, Al 5.15, Cl 19.59, C 3.63, H 0.43, N 5.00, with less than 50 ppm S. The nitrogen BET surface area of this activated catalyst was about 30 m.sup.2 /g with a pore volume of 0.06 cm.sup.3 /g.
This example demonstrates that a conventional catalyst prepared by a conventional potassium ferrocyanide-aluminum chloride process route does not produce catalyst compositions of the present invention, which are comprised of a dual colloid structure.
EXAMPLE 2 (COMPARATIVE)Catalyst B was prepared as follows:
A catalyst precursor composition was prepared according to the procedure of Example 1 hereof except a solution containing 187.67 g Al(NO.sub.3).sub.2.9H.sub.2 O in 500 ml H.sub.2 O was used instead of the AlCl.sub.3 solution. The resulting suspension had a pH of about 3 to 3.5.
After activating a portion of this material in accordance with the activation procedure of Example 1 hereof, it was examined by HREM and it was found to be made up of primarily two types of regions. The most prevalent region was one having substantially circular or spherical porous domains "necked" together and having particles in the size range of about 400 .ANG. to 4000 .ANG.. These domains had an internal porosity with most pores being of the order of about 100 .ANG.. In some of these porous spheres particles having a size of approximately 20 .ANG. were found. The second type of region, which comprised only about a third of the catalyst, contained metallic crystallites, most of which were imbedded in promoter particles. On average, these metal crystallites ranged in size from about 40 .ANG. to 1000 .ANG. along at least one dimension. The majority of these metal crystallites appeared to be between about 200 .ANG. and 400 .ANG. in diameter. The nitrogen BET surface area of the activated catalyst was about 9 m.sup.2 /g with a pore volume of 0.075 cm.sup.3 /g.
This example demonstrates that even when the preferred reagent, aluminum nitrate, is substituted for aluminum chloride of Example 1, the resulting catalyst composition is still not within the scope of the composition of the present invention. In fact, it was surprising that the compositions of this example had a substantially lower surface area than the compositions of Example 1. This was probably because most of the metal crystallites were engulfed in promoter particles.
EXAMPLE 3Catalyst C was prepared as follows:
A portion of the suspension of Example 2 hereof was diluted with an equal volume of water and refluxed for 40 hours under nitrogen. After cooling, the refluxed material was filtered and washed twice by repeating the sequence of resuspending the moist filter cake in 500 ml H.sub.2 O and filtering. The washed material was dried at reduced pressure at 50.degree. C. overnight then crushed and sieved.
A sample of this material was activated as in Example 1 hereof and examined by HREM where it was observed that 90% or more of the metal crystallites and promoter particles had a particle size between about 40 .ANG. and 100 .ANG. in diameter with less than one particle in 500 having a diameter greater than about 200 .ANG..
The resulting catalyst had a nitrogen BET surface area of about 110 M.sup.2 /g and a pore volume of 0.46 cm.sup.3 /g.
This example demonstrates the importance of a heating step, such as refluxing, for preparing the catalyst compositions of the present invention.
EXAMPLE 4Catalyst D was prepared as follows:
A solution of 30.0 g Al(NO.sub.3).sub.3.9H.sub.2 O, 20 g Mg(NO.sub.3).sub.2.6H.sub.2 O and 5.6 g Co(NO.sub.3).sub.2.6H.sub.2 O in 300 ml H.sub.2 O was rapidly mixed with 200 ml of H.sub.2 O with the simultaneous addition of a solution of 66.8 g K.sub.4 Fe(CN).sub.6.3H.sub.2 O in 300 ml of H.sub.2 O. The resulting green mixture, which had a pH of about 4.0 to 4.5, was refluxed for 40 hr under nitrogen. It was then cooled and filtered. The moist filter cake was washed twice with doubly distilled water and dried overnight at reduced pressure at 50.degree. C. The dried material was then crushed and sieved.
A sample of this material was activated according to Example 1 hereof and was examined by HREM which showed, as in the above example, that 90% or more of the metal crystallites and promoter particles had a particle size between about 40 .ANG. and 100 .ANG. in diameter with less than one particle in 500 having a dimension greater than about 200 .ANG.. This was confirmed by powder X-ray diffraction. Elemental analysis revealed that the active catalyst had the following composition (wt.%): Fe 28.71, Co 3.81, K 14.39, Mg 4.78, Al 6.97, C 4.54, H 0.39, N 8.9, with about 0.1% Cl and less than 42 ppm S. The empirical formula of the active catalyst was Fe.sub.2.0 Co.sub.0.25 K.sub.1.46 Mg.sub.0.78 Al.sub.1.03 C.sub.2.6 H.sub.1.55 N.sub.2.53 O.sub.x. The BET surface area of the activated catalyst after use was 216 m.sup.3 /g with a pore volume of 0.93 cm.sup.3 /g.
This example also illustrates a dual colloid catalyst composition of the present invention.
EXAMPLE 5Catalyst E was prepared as follows:
Solution A was prepared by dissolving 27.27 g Al(NO.sub.3).sub.3.9H.sub.2 O in 145 ml H.sub.2 O; the pH was 3.5. Solution B was prepared by dissolving 30.0 g K.sub.4 Ru(CN).sub.6.3H.sub.2 O in 145 ml H.sub.2 O; the pH was 8.9.
Solution A was added to 182 ml H.sub.2 O and vigorously mixed, then solution B was added. A blue-gray suspension with a pH of 4.2 resulted and was refluxed under nitrogen for 72 hours. The resulting suspension was allowed to cool to about room temperature then filtered to yield a filter cake which was resuspended in 1000 ml H.sub.2 O and refiltered. The final filter cake was dried overnight at reduced pressure at 50.degree. C. Elemental analysis of the dried solid gave the following (wt.%): 26.0 Ru, 5.1 K, 5.3 Al, 15.53 C, 19.31 N, 28.49 O and 1.0 H.
Powder X-ray diffraction results obtained in this material were consistent with small crystallites (about 100 .ANG.) of a RuRu(CN).sub.6 type material which may contain variable amounts of K and H.sub.2 O as well as trace amounts of Al. The majority of Al and K were believed to be present in an amorphous hydrous mixed oxide phase.
A 5 cm.sup.3 sample of this precursor material was activated under a flow of 500 SCCM N.sub.2, 1000 SCCM H.sub.2 and about 300 SCCM 95% H.sub.2 and 5% NH.sub.3 at about 1 atm total pressure. The bed was heated at 15.degree. C./hr from 35.degree. C. to 130.degree. C. and held there for nine hours. The H.sub.2 /NH.sub.3 mixture was then turned off and the reactor pressure increased to 4.2 MPa. The temperature was increased at 10.degree. C./hr to a set point temperature of 315.degree. C. and a maximum bed temperature of about 320.degree. C. The temperature of 320.degree. C. was held there for about 58 hours. The reactor temperature was then increased at 17.degree. C./hr to 380.degree. C. and the H.sub.2 and N.sub.2 flows adjusted to about 2.6 H.sub.2 /l N.sub.2.
A sample of the activated catalyst was examined by HREM which showed hexagonal Ru crystallites of about 15 .ANG. to about 200 .ANG. with the majority being from about 30 .ANG. to about 100 .ANG. in size interspersed with indistinct promoter particles of from about 30 .ANG. to 50 .ANG.. This was confirmed by powder X-ray diffraction. Elemental analysis revealed that the active catalyst had the following composition (wt.%): 35.1 Ru, 7.3 K, 10.9 Al, 2 C, 1.72 N, 1.72 H and 38.28 O.
This is an example of a ruthenium based dual colloid catalyst of the present invention.
EXAMPLE 6Catalyst F was prepared as follows:
Three solutions designated as A, B and C, respectively, were prepared as follows:
Solution A: 15.0 g Al(NO.sub.3).sub.3.9H.sub.2 O was dissolved in 80 ml distilled H.sub.2 O;
Solution B: 16.5 g K.sub.4 Ru(CN).sub.6.3H.sub.2 O was dissolved in 80 ml distilled H.sub.2 O; and
Solution C: 8.45 g K.sub.4 Fe(CN).sub.6.3H.sub.2 O in 60 ml distilled H.sub.2 O.
Solutions A and B were simultaneously added to 100 ml of distilled H.sub.2 O and vigorously mixed. Solution C was then added, again with vigorous mixing. The mixture was refluxed under nitrogen for 48 hours, then filtered and dried. The resulting catalyst precursor was then crushed and sieved and a portion of a 20-80 mesh fraction was activated in accordance with the activation procedure of Example 5 hereof.
A sample of the activated catalyst was examined by HREM which showed hexagonal Fe-Ru crystallites with a mean size of about 45 .ANG. with the following distribution:
______________________________________
Size Range, % of
.ANG. crystallites
______________________________________
4 to 25 9.8%
25 to 40 31.7%
40 to 60 35.3%
60 to 80 19.5%
80 to 180 3.7%
______________________________________
The total number of crystallites between 25 .ANG. and 80 .ANG. was equal to about 86.5%. Most promoter particles (99%) were between 30 and 100 .ANG. in size with 1% up to 750 .ANG.. Elemental analysis revealed that the active catalyst had the following composition (wt.%): 1.89 C, 2.7 N, 15.9 Fe, 19 Ru, 18.7 K, 16.1 Al, 25.9 O.
This is an example of an Fe Ru based dual colloid catalyst of the present invention.
EXAMPLE 7Catalyst G was prepared as follows:
A portion of the filter cake from Example 4 hereof was redispersed in 500 ml 0.1N NH.sub.4 NO.sub.3 solution and filtered, then redispersed in 500 ml 0.1M Ca(NO.sub.3).sub.2 solution, filtered, then washed with about 200 ml distilled water and dried overnight at reduced pressre at 50.degree. C. The dried material was then crushed and sieved and a portion of a 20-80 mesh fraction was activated in accordance with the activation procedure of Example 1 hereof. The activated material was examined by HREM and was found to have a structure similar to that of the material of Example 3 hereof.
After activation in accordance with the procedure of Example 1 hereof, the elemental composition was (wt.%): Fe 35.05, Co 4.81, K 5.63, Al 9.71, Mg 2.63, Ca 0.96, C 0.80, H 1.04, N 2.80, Cl<0.005, and S<0.002.
The emperical formula of the active catalyst was Fe.sub.2.0 Co.sub.0.25 K.sub.0.46 Mg.sub.0.34 Ca.sub.0.07 Al.sub.1.15 C.sub.0.21 N.sub.0.64 H.sub.3.28 O.sub.x
This example illustrats that the K level may be decreased and Ca introduced by ion-exchange.
EXAMPLE 8Catalyst H was prepared as follows:
A solution of 30.0 g Al(NO.sub.3).sub.3.9H.sub.2 O, 18.4 g Ca(NO.sub.3).sub.2.4H.sub.2 O and 5.6 g Co(NO.sub.3).sub.2.6H.sub.2 O in 300 ml H.sub.2 O and a solution of 66.8 g K.sub.4 Fe(CN).sub.6.3 H.sub.2 O in 300 ml H.sub.2 O were simultaneously added to 200 ml H.sub.2 O with vigorous mixing. The resultant green mixture had a pH of 4.0 to 4.5 and was refluxed under N.sub.2 for 40 hours. It was cooled under N.sub.2 and filtered. The resulting moist filter cake was divided into two approximately equal portions. The first portion was washed twice with doubly distilled water by resuspension and filtering and the other portion was used for preparing catalyst I of Example 9 hereof. The final filter cake was dried overnight at 50.degree. C. and reduced pressure then crushed and sieved.
After activation in accordance with the procedure of Example 1 hereof this catalyst was also examined by HREM and was found to have a structure similar to that of Example 3 hereof.
EXAMPLE 9Catalyst I was prepared as follows:
A portion of the filter cake from Example 8 hereof was resuspended in 500 ml NH.sub.4 NO.sub.3 solution and gently stirred overnight. The suspension was filtered and the resulting moist filter cake was resuspended in 200 ml H.sub.2 O, filtered, and the final filter cake dried overnight at reduced pressure at about 50.degree. C. The dried precursor was crushed and sieved and a 20 to 80 mesh fraction was activated in accordance with Example 1 hereof and examined by HREM.
EXAMPLE 10 (COMPARATIVE)Catalyst J was prepared as follows:
A precursor was prepared as described in U.S. Pat. No. 4,348,370. That is, 8.0 g of silica gel was added to a solution containing 3.43 g K.sub.4 Ru(CN).sub.6.3H.sub.2 O dissolved in 9.0 ml H.sub.2 O. This was mixed well and dried at 110.degree. C.
5.0 cm.sup.3, (4.39 g) of less than 80 mesh precursor was blended with 5.0 cm.sup.3, (5.92 g) 35 to 80 mesh fused quartz and charged to a reactor as in Example 1. With hydrogen flowing at 1445 SCCM, the reactor was rapidly heated to 125.degree. C., then pressurized to 1.7 MPa, whereupon the temperature was increased at 20.degree. C./hr to 425.degree. C. Once at 425.degree. C. the system was depressurized then repressurized with nominally 1H.sub.2 /1N.sub.2 synthesis gas.
EXAMPLE 11 (COMPARATIVE)Catalyst K was prepared as follows:
A precursor was prepared as taught in U.S. Pat. No. 4,348,370. That is, 15.9 g of 10 to 40 mesh gamma alumina having a surface area of 231 m.sup.2 /g and a pore volume of 0.585 cm.sup.3 /g was added to a solution of 3.5 g K.sub.4 Ru(CN).sub.6.3H.sub.2 O in 11 ml H.sub.2 O. The moistened solid was dried for 4 hours at 110.degree. C.
5.0 cm.sup.3, (3.95 g) of this precursor material was diluted with 5.0 cm.sup.3, (5.88 g) 35 to 80 mesh fused quartz, charged into a reactor and activated as in Example 9 hereof.
EXAMPLE 12 (COMPARATIVE)Catalyst L was prepared as follows:
This catalyst was prepared as taught in U.S. Pat. No. 4,348,370. 20 g of powdered gamma alumina having a surface area of 231 m.sup.2 /g and a pore volume of 0.585 cm.sup.3 /g was slurried with a solution of 3.4 g cobaltous acetate in 50 ml H.sub.2 O. To this slurry 3.2 g K.sub.4 Ru(CN).sub.6.3H.sub.2 O dissolved in 30 ml H.sub.3 O was added. Then 1.7 ml of glacial acetic acid was added. The resulting purple suspension was dried at 50.degree. C. and reduced pressure overnight. 5.0 cm.sup.3, (2.89 g) of less than 80 mesh precursor was blended with 5.0 cm.sup.3, (6.00 g) of 35 to 80 mesh fused quartz, charged to a reactor, and activated with hydrogen as in Example 9 hereof.
EXAMPLE 13Catalyst M was prepared as follows:
A solution containing 15.0 g Al(NO.sub.3).sub.3.9H.sub.2 O dissolved in 180 ml H.sub.2 O was rapidly mixed with a solution containing 16.5 g K.sub.4 Ru(CN).sub.6 H.sub.2 O dissolved in 80 ml H.sub.2 O. The resulting blue suspension which had a pH of 4.0, was then rapidly mixed with a solution of 6.6 g K.sub.3 Co(CN).sub.6.H.sub.2 O dissolved in 60 ml H.sub.2 O. The resulting blue mixture now had a pH of about 4.3. It was refluxed under N.sub.2 for 48 hours, cooled, filtered, and resuspended in 1000 ml H.sub.2 O, recovered by filtration, and dried overnight. A powder X-ray diffraction pattern obtained on this precursor was consistent with small (about 100.ANG.) Co-doped "ruthenium purple" crystallites.
Furthermore the powder X-ray diffraction pattern obtained from the activated material was consistent with the dual colloid structure of the present invention containing RuCo crystallites and an amorphous promoter. The activated material had a surface area of about 190 m.sup.2 /g and a pore volume of about 0.6 cm.sup.3 /g.
Elemental analysis revealed that the active catalyst had the following composition (wt.%):
Ru 42.07, Co 0.73, K 9.98, Al 14.24, C 0.69, H 0.92, N 4.67, S 0.0084, Cl 0.0038 and the balance oxygen.
This is an example of a CoRu-based dual colloid catalyst in accordance with the present invention.
EXAMPLE 14Catalyst N was prepared as follows:
A solution containing 32.0 g Al(NO.sub.3).sub.3.9H.sub.2 O, 24 g Mg(NO.sub.3).sub.2.6H.sub.2 O and 1.0 g Co(NO.sub.3).sub.2 in 350 ml H.sub.2 O was rapidly mixed with a second solution and with 100 ml H.sub.2 O with the aid of an ultrasonic blender. The second solution contained 66.0 g K.sub.4 Fe(CN).sub.6.3H.sub.2 O, 30.4 g K.sub.3 Co(CN).sub.6.H.sub.2 O and 9.4 g K.sub.4 Ru(CN).sub.6.3H.sub.2 O in 650 ml H.sub.2 O. The resulting blue-green mixture had a pH of 5.1 and turned yellow-green after a few minutes. Half of this mixture was refluxed for 48 hours under N.sub.2. The mixture was cooled and turned blue upon exposure to air. It was thoroughly mixed with 5.9 g of colloidal yttria in 300 ml H.sub.2 O (15.7% Y.sub.2 O.sub.3 colloidal suspension). The mixture was then centrifuged at 4000 rpm for 15 minutes and the solid resuspended in 1000 ml H.sub.2 O. The centrifugation/washing precedure was repeated three times and the final solid was resuspended in a minimum of water and filtered. The resulting moist filter cake was extruded into 2 mm diameter random length cylinders and dried overnight at 50.degree. C. at reduced pressure, 5.0 cm.sup.3 (3.5 g) of the solid was blended with 5.0 cm.sup.3 (5.0 g) of crushed quartz and charged into a tubular reactor.
After activation in accordance with the procedure of Example 1 hereof, the activated material was examined by HREM which showed that at least about 90% of the metal crystallites and promoter particles were between about 30.ANG. and 100.ANG., with most being less than about 75.ANG.. The activated catalyst was found by elemental analysis to contain the following (wt.%): 16.1 Fe, 0.68 Co, 2.8 Ru, 16.7 K, 4.3 Al, 3.7 Mg, 3.0 Y, 5.7 C, 1.9 H, 4.5 N, balance oxygen.
EXAMPLES 15-28In these Examples, catalysts of the above Examples were used for ammonia synthesis. In all of these examples the corresponding catalyst precursor was crushed and sieved to 20 to 80 mesh while the fused quartz diluent used was 20 to 35 mesh. Although the diluent is unnecessary for ammonia synthesis, it serves the experimental purpose of decreasing and smoothing out the adiabatic temperature rise in the catalyst bed caused by the exothermic ammonia synthesis reaction. The reactor employed had three cylindrical brass jackets tightly clamped along its length. The central brass cylinder, which spanned the reaction zone, helped to distribute the temperature increase caused by the ammonia synthesis reaction. The reactor tube was 0.50" O.D. by about 0.4" I.D. and it was equipped with an 0.0625" O.D. axial thermowell for a travelling thermocouple. The reactor was used in an upflow mode with the feed gas preheated by passage through a length of 0.125" O.D. tubing. The reactor was charged with 7.5 cm.sup.3 of inert porcelain spheres above the thermowell centering disk. The spheres served to support the catalyst bed and to further preheat the reactant gas mixture. For most of these ammonia synthesis examples, except when indicated otherwise, the reaction was conducted with approximately 3 H.sub.2 /1 H.sub.2 synthesis gas. The temperature reported for the reactions corresponds to the hottest part of the catalyst bed and the gas compositions reported were measured at the reactor outlet by gas chromatography. The space velocity reported, except where otherwise indicated, was based on the volume of catalyst recovered from the reactor because of the different volumetric contractions for any specific catalyst precursor. The results are shown in Table I below.
TABLE I
__________________________________________________________________________
Temp
Gas Composition
Space
Pressure
Space Time Yield
Ex.
Catalyst
.degree.C.
H.sub.2
N.sub.2
NH.sub.3
Velocity
MPa g NH.sub.3 /liter Cat/hr.
__________________________________________________________________________
15 A 393 72.3
22.2
5.5
9054 4.33 357
344 73.9
22.9
3.2
9176 4.34 216
16 B 392 73.7
23.1
3.1
8530 4.36 197
350 74.6
23.3
2.1
8530 4.36 132
17 C 392 71.1
22.0
7.0
9067 4.52 449
340 73.9
23.1
3.0
8874 4.54 209
18 D 392 68.9
21.0
10.2
8075 4.29 567
347 71.3
21.9
6.8
8075 4.29 411
19 E 389 61.3
24.6
14.0
17850
4.24 1770
371 63.4
25.1
11.5
17850
4.24 1450
340 69.4
26.6
3.9
17850
4.24 497
300 72.1
27.3
0.7
17850
4.24 88
371 36.8
49.5
13.7
17843
4.28 1730
(1/1 H.sub.2 /N.sub.2)
340 41.4
49.5
9.1
17843
4.28 1150
304 48.7
49.2
2.2
17843
4.28 274
340 18.0
72.4
9.6
17668
4.30 1200
(0.7/1 H.sub.2 /N.sub.2)
301 25.1
71.0
3.9
17668
4.30 485
20 F 380 69.3
20.0
10.7
8000 4.24 581
347 72.1
21.2
6.7
8000 4.24 381
21 G 393 68.9
21.5
9.6
11790
4.12 782
348 71.5
22.3
6.2
12249
4.13 544
22 H 392 69.2
21.6
9.2
7730 4.12 493
348 71.7
22.5
5.8
7800 4.16 325
23 I 398 68.5
22.8
8.7
10705
4.10 650
24 J 425 53.6
42.9
3.6
1412 1.87 37 (1/1 H.sub.2 /N.sub.2)
405 75.6
23.6
0.5
6816 4.11 27
25 K 425 49.0
46.5
4.6
1181 1.78 39 (1/1 H.sub.2 /N.sub.2)
402 75.7
23.6
0.6
6331 4.28 30
26 L 427 52.3
46.1
1.6
2359 1.70 30 (1/1 H.sub.2 /N.sub.2)
405 76.4
23.5
0.1
12736
4.39 11
27 M 342 72.36
24.22
3.43
25700
4.13 647
388 65.55
21.48
12.98
25700
4.13 2241
28 N 344 71.46
22.06
6.48
7240 4.18 334
388 69.32
20.96
9.72
7240 4.18 486
__________________________________________________________________________
EXAMPLES 29 TO 71
Dual colloid catalysts containing the elements set forth in Table II below for the active phase and the promoter phase were prepared by any one of four methods:
(1) Direct cyano-complex method of Example 4; (2) the cyano complex--ion exchange method of Example 8; (3) the addition of a colloidal suspension of a promoter element oxide or hydrous oxide to a suspension of cyano-complex precursor as prepared in accordance with Example 4; or (4) adding a preformed solid or slurry.
All of these catalysts were found to be active for ammonia synthesis.
TABLE II
______________________________________
Elements
Active Promoter
Example Phase Phase Method
______________________________________
29 FeCoRu KMgAl 1
30 FeNi KAlMgSr 2
31 FeNi KAlMg 1
32 RhRu KAlMgBa 1
33 FeRh KAlMgBa 1
34 FeCoAg KAlMg 2
35 FeCo KAlMgCa 2
36 FeCo KAlMgNa 2
37 FeCo KAlMgRb 2
38 FeCoRe KAlMg 2
39 FeCoMo KAlMg 1
40 FeCoNi KMgAl 1
41 FeCo KMgCr 1
42 FeCoW KAlMgSi 1
43 FeMn KAlMg 1
44 FeCo SrMgAl 1
45 FeCoW KAlMg 2
46 FeCoMo KAlMg 2
47 FeCo KAlMgZr 2
48 FeCo KAlMgLa 2
49 FeCo KAlMgCe 2
50 FeCo KalMgSi 3
51 FeCo KAlMgBa 1
52 FeMo KAl 1
53 FeRuRe KAl 1
54 FeRu KCe 1
55 FeRu KAl/MgSi 4
56 FeCo KAlMgCr 1
57 FeCo KLiAlMg 1
58 FeCo KMgAlSi 1
59 FeCo KAlMgBa 2
60 FeCo KAlMgSr 2
61 FeCo KMgAlEu 1
62 FeCo KMgAlLa 1
63 FeCo KMgAlCe 1
64 FeCo KMgAlSr 1
65 FeCo KSrAl 1
66 FeCo KCsMgAl 1
67 FeCo KCsMgAlSr 2
68 FeCo KMgSrBaAl 2
69 FeCo KMgAlBa 2
______________________________________
The following were prepared and activated similar to that in Example 4 but with In(NO.sub.3).sub.3 or Ga(NO.sub.3).sub.3 replacing Al(NO.sub.3).sub.3 and were found to be inactive for NH.sub.3 synthesis:
______________________________________
70 FeCoIn KMg 1
71 FeCoGa KMg 1
______________________________________
EXAMPLE 73
A dual colloid catalyst precursor with the empirical formula Fe 0.93, Co 0.001, K 0.41, Al 1.0, C 2.97, N 3.37, H 3.56, O 2.77, was activated with 75% H.sub.2 and 25% N.sub.2 at a GHSV of 1500 under 0.9 MPa by heating from 130.degree. C. to 315.degree. C./hr and then holding at 315.degree. C. for 18 hours before increasing the temperature at 20.degree. C./hour to 400.degree. C. and holding at 400.degree. C. for 4 hours. It was then conditioned for Fischer-Tropsch synthesis by lowering the temperature to 220.degree. C., increasing the pressure to 2.0 MPa and changing the gas composition to 45% H.sub.2, 45% CO and 10% N.sub.2 and decreasing the GHSV to 500.
The temperature was increased to 230.degree. C. after 12 hours at 220.degree. C. The following results were obtained after two hours at 230.degree. C. 85% CO conversion was achieved with 69% selectivity to CO.sub.2 and 31% selectivity to a mixture of hydrocarbons and oxygenated products. These were distributed on a carbon molar basis as follows: 31% CH.sub.4, 4.3% C.sub.2 H.sub.6, 10.6% C.sub.2 H.sub.4, 3.0% C.sub.3 H.sub.8, 23% C.sub.3 H.sub.6, 6.3% C.sub.4 H.sub.10, 9.3% C.sub.4 H.sub.8 and 35% of a mixture of C.sub.5 hydrocarbons and some alcohols and other oxygenated products. About 76 mole % of the C.sub.2 to C.sub.4 gaseous products were olefinic.
After 12 hours the temperature was again reduced to 220.degree. C. After 6 hours at these conditions the CO conversion was 46.3%, with 65.4% molar carbon selectivity to CO.sub.2 and 34.6% selectivity to hydrocarbon and oxygenates. The distribution of the hydrocarbons and oxygenates on a molar carbon basis was 6.5% CH.sub.4, 3.1% C.sub.2 H.sub.6, 20.7% C.sub.2 H.sub.4, 4.3% C.sub.3 H.sub.8, 16.0% C.sub.3 H.sub.6, 5.1% C.sub.4 H.sub.10, and 13.0% C.sub.4 H.sub.8 with 41.3% C.sub.5 + hydrocarbons and oxygenates. On a molar basis 67.6% of the C.sub.1 to C.sub.4 hydrocarbon gas produced was olefinic. The waxy portion of the product under these conditions contained 28 wt.% C.sub.5 to C.sub.20 terminal olefins, 19.5% C.sub.8 to C.sub.20 n-paraffins and 12.5 wt.% C.sub.5 to C.sub.20 alcohols. The hydrocarbons heavier than C.sub. 16 contained less than 50% terminal olefins.
The reactor temperature was maintained at 220.degree. C. for 24 additional hours, although after 12 hours the gas composition was changed to 10% N.sub.2, 33.75% H.sub.2 and 56.75% CO. Six hours later the temperature was increased to 230.degree. C. and held for 6 hours. The system was then treated at about 500 GHSV with 90% H.sub.2, 10% N.sub.2 at 0.9 MPa at 400.degree. C. for 12 hours. Finally, still at 0.9 MPa, the feed gas composition was changed to 10% N.sub.2, 57.9% H.sub.2 and 32.1% CO. After 4 hours at 220.degree. C. and 3 hours at 230.degree. C. the catalyst gave 39% CO conversion with 51% selectivity to CO.sub.2 and 49% to other products. The other products were distributed on a carbon molar basis as follows: 7.5% CH.sub.4, 17.0% C.sub.2 H.sub.6, 6.8% C.sub.2 H.sub.4, 4.0% C.sub.3 H.sub.8, 17.0% C.sub.3 H.sub.6, 2% C.sub.4 H.sub.10, 2.3% C.sub.4 H.sub.8, 12.6% C.sub.5 products and about 34% C.sub.6 hydrocarbons and oxygenates.
The combined C.sub.14 plus wax fraction produced over 20 hours with 57.9% H.sub.2, 32.1% CO and 10% N.sub.2 at 0.9 MPa and 500 GHSV at from 21% CO conversion (220.degree. C.) to 50% CO conversion (224.degree. C.) may be characterized as having hydrocarbon distribution equivalent to a Flory-Schultz alpha value of 0.92 over the range of C.sub.14 to C.sub.35, with about 14 wt.% of the wax in the C.sub.36 to C.sub.50 range and some 4 wt.% of the wax being heavier than 50.
EXAMPLE 75A catalyst precursor with the emperical formula Fe 1.7, Co 0.11, K 0.69, Mg 0.67, Al 1.0, C 8.46, H 26.85, O 15.95 was prepared in a manner similar to Catalyst D, Example 4, but with ion-exchange with 234 g NH.sub.4 NO.sub.3 in 200 ml of water, repeated twice, to reduce the potassium level. It was activated then treated with 1CO/1H.sub.2 at 0.9 MPa and 220.degree. C. for 12 hours, 230.degree. C. for 24 hours and 240.degree. C. for 12 hours. This was followed by 8 hours at 400.degree. C. under 3H.sub.2 /1N.sub.2. The temperature was then reduced to 220.degree. C. under 1CO/1H.sub.2 at 500 GHSV and 0.9 MPa. After 12 hours at these conditions the catalyst gave 47% CO conversion with 48% selectivity to CO.sub.2 and 52% selectivity to hydrocarbon products. On a molar carbon basis the distribution of the hydrocarbon products were as follows: 5.7% CH.sub.4, 3.2% C.sub.2 H.sub.6, 5.5% C.sub.2 H.sub.4, 2.8% C.sub.3 H.sub.8, 5.1% C.sub.3 H.sub.6, 3.3% C.sub.4 H.sub.10, and 7.6 C.sub.4 H.sub.8 with 66.8% C.sub.5 + and oxygenated products.
Claims
1. A method for preparing catalyst precursor compositions which upon activation results in a catalyst containing one of more reducible metallic phases and one or more non-reducible promoter phases which method comprises:
- (a) forming a gel or suspension by admixing; (i) one or more transition metal cyano-containing anionic-complex solutions wherein at least on solution contains one or more reducible transition metals selected from the Groups IB, IIB, VIB, VIIB, VIII of the Periodic Table of the Elements, wherein the cations accompanying the anionic complexes may be one or more alkali metal ions, with (ii) one or more solutions containing metal cations wherein at least one of the metals is a nonreducible metal selected from the group consistion of Cr, Al, Th, U, Si, the lanthanides, and elements of Group IA, IIA, IIIB, IVB and VB of the Periodic Table of the Elements;
- (b) heating the resulting gel, or suspension, at a temperature of about 90.degree. C. to about 150.degree. C. for an effective amount of time to allow hydrolysis and polymerization to occur;
- (c) separating and drying the resulting solid precursor.
2. The method of claim 1 wherein the precursor is activated by heating it at less than 1.degree. C./minute to between about 315.degree. C. and 500.degree. C. in a hydrogen containing atmosphere and holding it at that temperature for an effective amount of time.
3. The method of claim 2 wherein the active catalyst is characterized as comprising:
- (a) from about 15 to about 85 wt.% of crystallites selected from the group consisting of (i) crystallites of one or more transition metals and (ii) crystallites of reducible transition metal carbides, nitrides, and oxides, and mixtures thereof, said transition metal being selected from those reducible metals from Groups IB, IIB, VIB, and VIII of the Periodic Table of the Elements, wherein at least 80% of the crystallites have a diameter, d, between about 25.ANG. and 500.ANG. with the proviso that the crystallite size distribution of at least about 80% of these be expressed by the relationship 0.5D<d<2D where D is the median of the diameters of this 80%; and
- (b) from about 15 to about 85 wt.% of a nonreducible promoter phase interspersed with the metal crystallites and containing at least one element selected from the group consisting of Cr, Al, Si, Th, U, the lanthanides, and Group IA, IIA, IIIB, IVB and VB of the Periodic Table of the Elements, wherein the promoter phase is comprised of particles of which at least about 80% have a diameter between about 15.ANG. and 1500.ANG. wherein the median diameter (D) of the metal crystallites and the median diameter of the 80% of the promoter particles do not differ by more than a factor of about 20.
4. The method of claim 3 wherein the transition metals are selected from the group consisting of Fe, Co, Ni, and Ru and the nonreducible promoter phase elements are selected form the group consisting of Mg, Ca, Sr, Ba, Li, Na, K, Rb, Cs, Y, La, Ce, Eu, Th, U, the remaining lanthanides, Ti, Zr, Hf, Nb, Ta, Cr, Al and Si.
5. The method of claim 4 wherein one or both of Al and Si are present as promoter phase elements.
6. The method of claim 3 wherein the transition metals are selected from the group consisting of Fe, Ru, Co, Ni, Mo, W and Mn, and the nonreducible promoter phase elements are selected from the group consisting of Mg, Ca, Sr, Ba, Li, Na, K, Rb, Cs, La, Ce, Ti, Zr, Hf, Nb, Ta, Si, Al, Cr and Y.
7. The method of claim 6 wherein the transition metals are Fe and Co.
8. The method of claim 6 wherein the transition metals are Fe and Ni.
9. The method of claim 6 wherein the transition metals are Fe, Mo, and W.
10. The method of claim 6 wherein the transition metals are Fe and Ru.
11. The method of claim 6 wherein the transition metal is Fe only.
12. The method of claim 6 wherein the transition metal is Ru only.
13. The method of claim 6 wherein the transition metals are Fe, Ru, and Co.
14. An activated catalyst prepared in accordance with claim 2.
15. A catalyst precursor composition prepared in accordance with claim 1.
16. An activated catalyst prepared in accordance with claim 4.
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Type: Grant
Filed: Aug 10, 1984
Date of Patent: May 13, 1986
Assignee: Exxon Research and Engineering Co. (Florham Park, NJ)
Inventors: Thomas H. Vanderspurt (E. Amwell Twp., Hunterdon County, NJ), Michael A. Richard (Fanwood, NJ)
Primary Examiner: W. J. Shine
Attorney: Henry E. Naylor
Application Number: 6/639,443
International Classification: B01J 2104; B01J 2108; B01J 2346; B01J 2374;
